Jet mills and the like



Oct. 24, 1961 H. VOGEL ETAL JET MILLS AND THE LIKE Filed Feb. 16, 1960FIG I IN V EN TORS N mm N MZ G H O V H D T T UWHM MTB amm HMHM Y I B 2 lF THEIR ATTORNEYS United States Patent 3,005,594 JET MILLS AND THE LIKEHelmnt Vogel and Martin Hartmann, Wolizenbuttel, and

Herbert Spitzner, Berlin-Wilmersdorf, Germany, assignors to ScheringA.G., Berlin, Germany, a corporation of Germany Filed Feb. 16, 1960,Ser. No. 8,954 Claims priority, application Germany Feb. 24, 1959 8Claims. (Cl. 241-39) I This invention relates to jet mills, and thelike.

Iet mills for the very fine grinding of solids are already known. Theyoperate in accordance with the principle of the impact mill, theacceleration of the material to be ground being effected not bymechanically moved parts of the apparatus, but rather by the energy ofgas or vapor jets which expand into the grinding chamber. They can, forinstance, be constructed ina manner that a round or disc-shaped grindingchamber is provided on its top with a tangentially directed injectornozzle for the introduction of the material to be ground; or on itsperiphery with a large number of inlet nozzles for the propellant gas,which nozzles are directed tangentially thereto inthe same direction,and in the center with an outlet opening for the discharge of the groundmaterial and the expanded propellant gas.

In commercial types of'jet mills, the diameter of the grinding chambercan be about 50 to 1200 mm and its height about 25m 62 mm. There areused about 3 to 16 propellant nozzles, the outlet openings of which mayhave a diameter of 1.4 to 6 mm. As propellants, air, superheated steamor other gases of a pressure of about 3 to 10 atmospheres gauge areused. The ground material is deparated in a subsequent cyclone with orwithout a filter.

Such jet mills are used particularly for very finely comminutingsubstances which are sensitive to heat and chemicals and-in which highrequirements as to fineness and uniformity of the grain as well aspurity are necessary. In operating such mills in actual practice, it hashowever, been' found that many substances which absolutely require sucha gentle grinding, for instance plant protective agents, pharmaceuticalsubstances, etc., cannot be dependably comminuted with a satisfactoryquantitative output. A crust is formed, predominantly in the outer zonesof the grinding chamber, so that the feeding of the propellant and theremoval of the fine dust become irregular and pieces of crust which havebroken oil are contained in the final product. This situation can sometimes be improved by strongly reducing the feed of the material to beground while keeping the amount of propellant unchanged, by frequentlyopening and cleaning the grinding chamber and by drying the propellantbefore its introduction into the grinding chamber, which, however,impairs the economy of the grinding process.

It is an object of the present invention to overcome the above noteddisadvantages.

Another object of the present invention is to provide a jet mill inwhich the lateral wall of the grinding space thereof is developed in astepwise manner.

Another object of the present invention is to provide a mill having atthe top of the grinding chamber, a device which makes possible avariable adjustment of the injector nozzle in such a manner that thehorizontal angle between the axis of the nozzle and the radius of thegrinding chamber is variable.

Still another object of the present invention is to provide a millhaving a valve or a similar device which is so developed that it makespossible the closing of the discharge opening for the ground materialand propellant one or more other openings which open into the grindingchamber being simultaneously exposed.

Other objects will become apparent from the following detaileddescription taken in conjunction with the accompanying drawing, inwhich:

FIGS. 1 and 2 show schematically, by Way of example, of a preferredembodiment sections through the mill obtained when employing theinventive concept.

A grinding chamber A, FIG. 1, has an outer circular periphery and theinterior has, for instance, three recessed portions forming circularsteps, 10, 11 and 12 respectively. A central outlet pipe B extends fromthe bottom of chamber A for the mixture of propellant of groundmaterial, while a feed opening C for the material to be ground ismounted on eccentric disc H The propellant, which at the same timeserves to feed the injector nozzle D disposed at the opening C, entersthe mill at areas E, F andG and after emerging from the tangentialnozzles or'boreholes d, e, f, and g,-expands down to a pressure slightlyabove atmospheric pressure.

' On the top of the grinding chamber, there are provided, two eccentricdiscs H and H FIGS. 1 and 2, by means of which a change of the angle a,FIG. 2 between the axis of the injector nozzle and the chamber radius ispossible. By turning disc H through angle a theaxis of the injectornozzle can be brought from the direction R into the direction R while byturning the disc H through an angle of 90 it can be brought from R intothe direction R Upon the turning from R towards R the length of the pathof the jet until it impinges upon the wall of the grinding chamber isalso changed, which is of great importance in order to prevent theformation of a crust during the pulverizing operation.

"Although the formation of a crust is very substantially prevented bythe development, in accordance with the invention, of the cross-sectionof the grinding chamber and the possibility of varying the angle atwhich the material to be ground is charged, it is nevertheless possible,in the case of substances which are very difiicult to grind or whichtend readily to bake-on, that crusts will form after longer periods "ofoperation; These crusts can be removed without'the cumbersome removal ofentire parts of the apparatus being necessary as was formerly .the'case.It is merely necessary to lower the valve plate K which is mounted on anoutwardly open tubular guide member M guided in a stufling box 3', FIG.1, and formed with openings L axially spaced from the valve plate K. Inthis manner, the connection cap B is tightly closed and the openings Lin the tubular guide member M are exposed. Flushing or drying of thegrinding chamber can now be elfected with any desired liquids, vapors orgases which are fed for instance to the connections D, E, F and Ggrinding chamber.

The preferred embodiment described above of the improvements inaccordance with the invention constitute merely one example. There aremany possibilities of structural variation which fall within the scopeof the invention and which are to be employed in the specific case. Thusthe grinding chamber may have merely two or more than three steps andthe inlet nozzles can be present on all or only a few of the steps.

Excellent advantages of the invention have been shown by theefiectiveness of the measure and proven by numerous tests on a grindingchamber, the outer wall of which had three steps of a diameter of 550mm., 450 mm. and 350 mm. respectively, each of a height of 20 mm. andwhich was provided with a total of 54 tangential propellant nozzles inwhich compressed air of an initial pressure of 7 atmospheres gauge wasexpanded. As material to be ground, there were employed varioussubstances which had always given difficulties in other devices due tothe formation of a crust and the breaking off of crusts when ground inthe previously known J'Q mills of the I micronizer type. In eachcase, itwas found that the new type of mill could be'operated five to ten timeslonger before the formation of crusts .led to diificulties'in operation.Also the possibilityof adjusting'the angle of the feed nozzle to theoptimum value had a favorable influence on the reduction of thefiormation of crust and on the uniformity of the particle. size of thefinal product. Furthermore, the elimination of crusts was easilypossible by using the flushing device. Also the consumption ofcompressed air per kg. of material ground is not higher, and that thecapacity of the mill for the same diameter grinding chamber was about 2percent greater. 7

While a preferred form vof the invention has been described andillustrated, it is to be understood that changes or modifications as toform, arrangement of parts and use of materials may be made withoutdeparting from the spirit and scope of the invention as claimed.

' We claim:

1. A jet mill for finely grinding solids, comprising a cylindricalchamber, which'is provided with tangentially directed inlet nozzles forpropellant gas, said nozzles being arranged on the periphery of thechamber, an injector nozzle directed tangentially in .the same directionas the nozzles for the introduction of the material to be ground,

said chamber having 'a central outlet opening for the discharge of theground material .and of the expanded propellant gas, said chamber havinga pair of eccentrically mounted covers'for variable adjustment of'theinjector nozzle whereby the horizontalangle a between the nozzle axisand the radius of the grinding chamber is adjustable.

2. Ajet mill for the grinding or solids, comprising a chamber having anaxis and provided on the periphery with tangentially directedinletnozzles for propellant gas;

aninjector nozzle 'on the t'opuof the chamber directed tangentially inthe same direction as'the inlet nozzles for the introduction of thematerial to be ground, said chamber having'a central outlet opening forthe discharge of the ground material and of the expanded propellant gas,and closure 'means for closing the outlet opening tor ground materialand propellant, at least one opening in said closure means communicatingwith the grinding chamber being simultaneously exposed when said outlet:opening is being closed.

3 VA in ccording t aim 2, id m r ving an axially extending stepped wall,and said inlet nozzles for propellant gas beingmounted on said wall ofsaid chamber.

4. A jet mill for grinding solids comprising a chamber having an axis,an axially extending side wall, and a top wall transverse of said axis,said side wall having a substantially circular cross section decreasingstepwise in an axial direction away from said top wall; a plurality oftangentially disposed inlet nozzles in said chamber; injector nozzlemeans mounted on said top wall for injecting a material to be groundinto said chamber in a tangential direction relative to said axis; and adischarge conduit axially communicating with said chamber.

' 5. A jet mill as set forth in claim 4, wherein said inlet nozzles aredisposed tangentially in said tangential direction relative to saidaxis. V j

6. A jet mill as set forth in claim 4, further comprising a tubularguide member; valve plate'means mounted on said tubular member, saidmember being and formed with an openingispaced from said valve platemeans and slidably movable into and out of said chamber toward and awayfrom a position in which said valve plate means closes said dischargeconduit, and said opening communicates with the interior of saidchamber.

7. A jet millfas set forth in claim 4, wherein said side wall has aplurality of alternating radially and axially extending annularportions, two adjacent ones of portions jointly constituting a step insaid side wall respective ones of said inlet nozzles being mounted on aplurality of said steps. 7

8. Ajet as set forth in claim 4, further comprising pivot means on saidtop wall, said injector nozzle means being mounted on said pivot meansfor pivoting movement about an axis extending in the direction of theaxis of said chamber; 7

References Cited in the file of this patent STATES PATENTS 2.032.827Andrews. V Mar. 3., is; 2,155,697 Young Apr. 25, 1939 2,257,907 GriswoldOct. 7, 1941 2,690,880 'Chatelain o r. 5, 1954 n the

